U.S. patent application number 13/781233 was filed with the patent office on 2014-08-28 for power factor correction converter with current regulated output.
This patent application is currently assigned to Asahi Kasei Microdevices Corporation. The applicant listed for this patent is ASAHI KASEI MICRODEVICES CORPORATION. Invention is credited to Gabriel C. GAVRILA, Fernando Ramon MARTIN-LOPEZ, Takahiro UMEKI.
Application Number | 20140239810 13/781233 |
Document ID | / |
Family ID | 51387442 |
Filed Date | 2014-08-28 |
United States Patent
Application |
20140239810 |
Kind Code |
A1 |
MARTIN-LOPEZ; Fernando Ramon ;
et al. |
August 28, 2014 |
POWER FACTOR CORRECTION CONVERTER WITH CURRENT REGULATED OUTPUT
Abstract
A power factor correction converter in a buck-boost
configuration may include a set-up circuit configured to supply an
input voltage, a buck transistor connected to the set-up circuit,
and configured to receive a current from the diode bridge, a first
diode connected to the buck transistor, a boost transistor, a
resistor connected to the boost transistor, a coil that connects
the buck transistor and the boost transistor, a buck-boost PFC
regulator connected to the set-up circuit, and configured to
regulate a time pattern of the on/off status of the first
transistor and the second transistor synchronously, a second diode
connected to the coil and the boost transistor, and configured to
output a first level voltage, a capacitor connected to the second
diode and a load connected to the second diode.
Inventors: |
MARTIN-LOPEZ; Fernando Ramon;
(Colorado Springs, CO) ; GAVRILA; Gabriel C.;
(Colorado Springs, CO) ; UMEKI; Takahiro; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASAHI KASEI MICRODEVICES CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
Asahi Kasei Microdevices
Corporation
Tokyo
JP
|
Family ID: |
51387442 |
Appl. No.: |
13/781233 |
Filed: |
February 28, 2013 |
Current U.S.
Class: |
315/85 |
Current CPC
Class: |
H05B 45/37 20200101;
H05B 47/10 20200101; Y02B 20/30 20130101; Y02B 20/347 20130101;
Y02B 20/348 20130101 |
Class at
Publication: |
315/85 |
International
Class: |
H05B 37/02 20060101
H05B037/02 |
Claims
1. A power factor correction (PFC) converter in a boost
configuration followed by a buck regulator, comprising: a set-up
circuit configured to supply an input voltage, the set-up circuit
comprises: an alternating current (AC) source; an electromagnetic
interference (EMI) filter; and a diode bridge; a first coil
connected to the set-up circuit, and configured to receive a
rectified current from the diode bridge; a first transistor
connected to the first coil; a boost PFC regulator configured to
regulate a first time pattern of an on/off status of the first
transistor; a first diode connected to the first transistor, and
configured to output a first level voltage; a first capacitor
connected to the first diode; a buck converter configured to
receive the first level voltage from the first diode, and convert
the first level voltage to a second level voltage, the buck
converter comprises: a second transistor connected to the first
diode; a buck regulator connected to the second transistor; a
second diode connected to the second transistor; a second coil
connected to the second transistor, and configured to output the
second level voltage; a second capacitor connected to the second
coil; and a load connected to the second coil.
2. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator claim 1, wherein the
boost PFC regulator further comprises: a first pair of resistor
dividers connected to the output of the set-up circuit; a second
pair of resistor dividers configured to receive the first level
voltage at the output of a first diode; a first reference voltage
corresponding to the first level voltage at the output of a first
diode; a first error amplifier (EA) configured to compare the first
reference voltage with the first level voltage received at the
second pair of resistor dividers; a multiplier configured to
receive outputs of the first pair of resistor dividers and the
first EA; a first oscillator; and a first pulse width modulation
(PWM) comparator configured to receive outputs of the multiplier
and the first oscillator, and regulate the first time pattern of
the on/off status of the first transistor.
3. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 2, wherein if
the first level voltage received at the second pair of resistor
dividers is less than the first reference voltage, the first EA
amplifies its output via the multiplier, and the first PWM
comparator extends a first duty cycle to boost the first level
voltage; or if the first level voltage received at the second pair
of resistor dividers is greater than the first reference voltage,
the first PWM comparator shortens the first duty cycle to reduce
the first level voltage.
4. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 1, wherein the
load further comprises: a light-emitting diode (LED) string
comprising a plurality of diodes connected in series; and a
constant current source configured to maintain a constant load
current or an arbitrarily modulated load current flowing through
the LED string.
5. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 4, wherein the
LED string is configured to be a low-side connection when the anode
of the LED string is connected to the second coil, the cathode of
the LED string is connected to one end of the constant current
source, and the other end of the constant current source is
connected to ground, and the buck regulator further comprises: a
second reference voltage corresponding to an intended voltage drop
across the constant current source; a second EA configured to
compare the second reference voltage with a third level voltage
received at the cathode of the LED string; a second oscillator; and
a second PWM comparator configured to receive outputs of the second
EA and the second oscillator, and regulate a second time pattern of
the on/off status of the second transistor.
6. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 4, wherein the
LED string is configured to be a high-side connection when one end
of the constant current source is connected to the second coil, the
other end of the constant current source is connected to the anode
of the LED string, and the cathode of the LED string is connected
to ground, and the buck regulator further comprises: a second
reference voltage corresponding to an intended voltage drop across
the constant current source; a second EA configured to compare the
second reference voltage with a third level voltage transmitted by
a differential amplifier (DIF); a second oscillator; and a second
PWM comparator configured to receive outputs of the second EA and
the second oscillator, and regulate a second time pattern of the
on/off status of the second transistor.
7. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 5 or 6, wherein
if the third level voltage is less than the second reference
voltage, the second EA amplifies its output, and the second PWM
comparator extends a second duty cycle to boost the second level
voltage; or if the third level voltage is greater than the second
reference voltage, the second PWM comparator shortens the second
duty cycle to reduce the second level voltage.
8. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 1, wherein when
the first transistor is on, the first coil is configured to
accumulate received current, or when the first transistor is off,
the first coil is configured to transmit accumulated current and
output the first level voltage to the buck converter via the first
diode.
9. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 1, wherein the
boost PFC regulator is configured to achieve a high power factor
correction level by regulating the first time pattern of the on/off
status of the first transistor.
10. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 4, wherein the
second level voltage is regulated in a feedback loop comprising the
buck converter, the LED string and the constant current source.
11. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 1, wherein the
second level voltage is independent of the first level voltage.
12. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 1, wherein the
constant load current or the arbitrarily modulated load current
flowing through the LED string is independent of the current
flowing through the set-up circuit, the first level voltage and the
second level voltage.
13. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 1, wherein the
load further comprises: a light-emitting diode (LED) string
comprising a plurality of diodes connected in series; a current
sense resistor; and an optional disconnect switch with one end
connected to one end of the current sense resistor.
14. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 13, wherein the
LED string is configured to be a low-side connection when the anode
of the LED string is connected to the second coil, the cathode of
the LED string is connected to the other end of the current sense
resistor, and the other end of the optional disconnect switch is
connected to ground, and the buck regulator further comprises: a
second reference voltage corresponding to an intended voltage drop
across the current sense resistor; a second EA configured to
compare the second reference voltage with a third level voltage
received at the cathode of the LED string; a second oscillator; and
a second PWM comparator configured to receive outputs of the second
EA and the second oscillator, and regulate a second time pattern of
the on/off status of the second transistor.
15. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 13, wherein the
LED string is configured to be a high-side connection when the
other end of the current sense resistor is connected to the second
coil, the other end of the optional disconnect switch is connected
to the anode of the LED string, and the cathode of the LED string
is connected to ground, and the buck regulator further comprises: a
second reference voltage corresponding to an intended voltage drop
across the current sense resistor; a second EA configured to
compare the second reference voltage with a third level voltage
transmitted by a differential amplifier (DIF); a second oscillator;
and a second PWM comparator configured to receive outputs of the
second EA and the second oscillator, and regulate a second time
pattern of the on/off status of the second transistor.
16. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 14 or 15,
wherein if the third level voltage is less than the second
reference voltage, the second EA amplifies its output, and the
second PWM comparator extends a second duty cycle to boost the
second level voltage; or if the third level voltage is greater than
the second reference voltage, the second PWM comparator shortens
the second duty cycle to reduce the second level voltage.
17. A power factor correction (PFC) converter in a boost
configuration followed by a buck regulator comprising: a set-up
circuit configured to supply an input voltage, the set-up circuit
comprises: an alternating current (AC) source; an electromagnetic
interference (EMI) filter; and a diode bridge; a first coil
connected to the set-up circuit, and configured to receive a
current from the diode bridge; a first transistor connected to the
first coil; a boost PFC regulator configured to regulate a first
time pattern of the on/off status of the first transistor; a first
synchronous rectifier connected to the first transistor via a first
inverter and configured to output a first level voltage; a first
capacitor connected to the first synchronous rectifier; a buck
converter configured to receive the first level voltage from the
first synchronous rectifier, and convert the first level voltage to
a second level voltage, the buck converter further comprises: a
second transistor connected to the first diode; a buck regulator
connected to the second transistor; a second synchronous rectifier
connected to the second transistor via a second inverter; a second
coil connected to the second transistor, and configured to output
the second level voltage; and a second capacitor connected to the
second coil; and a load connected to the second coil.
18. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 17, wherein the
boost PFC regulator further comprises: a first pair of resistor
dividers connected to the output of the set-up circuit; a second
pair of resistor dividers configured to receive the first level
voltage at the output of the first synchronous rectifier; a first
reference voltage corresponding to the first level voltage at the
output of the first synchronous rectifier; a first error amplifier
(EA) configured to compare the first reference voltage with the
first level voltage received at the second pair of resistor
dividers; a multiplier configured to receive outputs of the first
pair of resistor dividers and the first EA; a first oscillator; and
a first pulse width modulation (PWM) comparator configured to
receive outputs of the multiplier and the first oscillator, and
regulate the first time pattern of the on/off status of the first
transistor in order to force the AC current to follow the AC
voltage so as to achieve high PFC level.
19. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 18, wherein if
the first level voltage is less than the first reference voltage,
the first EA amplifies its output via the multiplier, and the first
PWM comparator extends a first duty cycle to boost the first level
voltage; or if the first level voltage is greater than the first
reference voltage, the first PWM comparator shortens the first duty
cycle to reduce the first level voltage.
20. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 17, wherein the
load further comprises: a light-emitting diode (LED) string
comprising a plurality of diodes connected in series; and a
constant current source configured to maintain a constant load
current or an arbitrarily modulated load current flowing through
the LED string.
21. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 20, wherein the
LED string is configured to be a low-side connection when the anode
of the LED string is connected to the second coil, the cathode of
the LED string is connected to one end of the constant current
source, and the other end of the constant current source is
connected to ground; and the buck regulator further comprises: a
second reference voltage corresponding to an intended voltage drop
across the constant current source; a second EA configured to
compare the second reference voltage with a third level voltage
received at the cathode of the LED string; a second oscillator; and
a second PWM comparator configured to receive outputs of the second
EA and the second oscillator, and regulate a second time pattern of
the on/off status of the second transistor.
22. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 20, wherein the
LED string is configured to be a high-side connection when one end
of the constant current source is connected to the second coil, the
other end of the constant current source is connected to the anode
of the LED string, and the cathode of the LED string is connected
to ground; and the buck regulator further comprises: a second
reference voltage corresponding to an intended voltage drop across
the constant current source; a second EA configured to compare the
second reference voltage with a third level voltage transmitted by
a differential amplifier (DIF); a second oscillator; and a second
PWM comparator configured to receive outputs of the second EA and
the second oscillator, and regulate a second time pattern of the
on/off status of the second transistor.
23. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 21 or 22,
wherein if the third level voltage is less than the second
reference voltage, the second EA amplifies its output, and the
second PWM comparator extends a second duty cycle to boost the
second level voltage; or if the third level voltage is greater than
the second reference voltage, the second PWM comparator shortens
the second duty cycle to reduce the second level voltage.
24. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 1, further
comprises a plurality of loads connected to the second coil,
wherein the plurality of loads are connected in parallel, and each
of the plurality of loads further comprises: a light-emitting diode
(LED) string comprising a plurality of diodes connected in series;
and a constant current source configured to maintain a constant
load current or an arbitrarily modulated load current flowing
through the LED string.
25. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 24, wherein the
LED string is configured to be a low-side connection when the anode
of the LED string is connected to the second coil, the cathode of
the LED string is connected to one end of the constant current
source, and the other end of the constant current source is
connected to ground, and the buck regulator further comprises: a
second reference voltage corresponding to a lowest intended voltage
drop across the plurality of constant current sources; a second EA
configured to compare the second reference voltage with a third
level voltage received at the cathode of one of the plurality of
the LED strings; a second oscillator; and a second PWM comparator
configured to receive outputs of the second EA and the second
oscillator, and regulate a second time pattern of the on/off status
of the second transistor.
26. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 24, wherein the
LED string is configured to be a high-side connection when one end
of the constant current source is connected to the second coil, the
other end of the constant current source is connected to the anode
of the LED string, and the cathode of the LED string is connected
to ground, and the buck regulator further comprises: a second
reference voltage corresponding to a lowest intended voltage drop
across the plurality of constant current sources; a second EA
configured to compare the second reference voltage with a third
level voltage transmitted by a differential amplifier (DIF); a
second oscillator; and a second PWM comparator configured to
receive outputs of the second EA and the second oscillator, and
regulate a second time pattern of the on/off status of the second
transistor.
27. The power factor correction (PFC) converter in a boost
configuration followed by a buck regulator of claim 25 or 26,
wherein if the third level voltage is less than the second
reference voltage, the second EA amplifies its output, and the
second PWM comparator extends a second duty cycle to boost the
second level voltage; or if the third level voltage is greater than
the second reference voltage, the second PWM comparator shortens
the second duty cycle to reduce the second level voltage.
28. A power factor correction (PFC) converter in a buck-boost
configuration, comprising: a set-up circuit configured to supply an
input voltage, the set-up circuit comprises: an alternating current
(AC) source; an electromagnetic interference (EMI) filter that; and
a diode bridge; a buck transistor connected to the set-up circuit,
and configured to receive a current from the diode bridge; a first
diode connected to the buck transistor; a boost transistor; a
resistor connected to the boost transistor; a coil that connects
the buck transistor and the boost transistor; a buck-boost PFC
regulator connected to the set-up circuit, and configured to
regulate a time pattern of the on/off status of the buck transistor
and the boost transistor synchronously; a second diode connected to
the coil and the boost transistor, and configured to output a first
level voltage; a capacitor connected to the second diode; and a
load connected to the second diode.
29. The power factor correction (PFC) converter in a buck-boost
configuration of claim 28, wherein the load further comprises: a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series; and a constant current source configured to
maintain a constant load current or an arbitrarily modulated load
current flowing through the LED string.
30. The power factor correction (PFC) converter in a buck-boost
configuration of claim 29, wherein the LED string is configured to
be a low-side connection when the anode of the LED string is
connected to the second diode, the cathode of the LED string is
connected to one end of the constant current source, and the other
end of the constant current source is connected to ground, and the
buck-boost PFC regulator further comprises: a pair of resistor
dividers connected to the output of the set-up circuit; a reference
voltage corresponding to an intended voltage drop across the
constant current source; an error amplifier (EA) configured to
compare the reference voltage with a second level voltage received
at the cathode of the LED string; a multiplier configured to
receive outputs of the pair of resistor dividers and the EA; an
oscillator and current sense ramp generator configured to receive
the output of the boost transistor; a pulse width modulation (PWM)
comparator configured to receive outputs of the multiplier and the
oscillator and current sense ramp generator, and a driver that
connects the output of the PWM comparator with the buck transistor
and the boost transistor to synchronously regulate the time pattern
of the on/off status of the buck transistor and the boost
transistor.
31. The power factor correction (PFC) converter in a buck-boost
configuration of claim 29, wherein the LED string is configured to
be a high-side connection when one end of the constant current
source is connected to the second diode, the other end of the
constant current source is connected to the anode of the LED
string, and the cathode of the LED string is connected to ground,
and the buck-boost PFC regulator further comprises: a pair of
resistor dividers connected to the output of the set-up circuit; a
reference voltage corresponding to an intended voltage drop across
the constant current source; an error amplifier (EA) configured to
compare the reference voltage with a second level voltage
transmitted by a differential amplifier (DIF); a multiplier
configured to receive outputs of the pair of resistor dividers and
the EA; an oscillator and current sense ramp generator configured
to receive the output of the boost transistor; a pulse width
modulation (PWM) comparator configured to receive outputs of the
multiplier and the oscillator and current sense ramp generator, and
a driver that connects the output of the PWM comparator with the
buck transistor and the boost transistor to synchronously regulate
the time pattern of the on/off status of the buck transistor and
the boost transistor.
32. The power factor correction (PFC) converter in a buck-boost
configuration of claim 30 or 31, wherein if the second level
voltage is less than the reference voltage, the EA amplifies its
output via the multiplier, and the PWM comparator extends the duty
cycle to boost the first level voltage; or if the second level
voltage is greater than the reference voltage, the PWM comparator
shortens the duty cycle to reduce the first level voltage.
33. The power factor correction (PFC) converter in a buck-boost
configuration of claim 28, wherein when the buck transistor and the
boost transistor are on synchronously, the coil is configured to
accumulate received current; and when the buck transistor and the
boost transistor are off synchronously, the coil is configured to
transmit accumulated current and output the first level voltage via
the second diode.
34. The power factor correction (PFC) converter in a buck-boost
configuration of claim 28, wherein the buck-boost PFC regulator is
configured to achieve a high power factor correction level by
regulating the time pattern of the on/off status of the buck
transistor and the boost transistor synchronously.
35. The power factor correction (PFC) converter in a buck-boost
configuration of claim 29, wherein the first level voltage is
regulated in a feedback loop comprising the second diode, the
capacitor, the LED string and the constant current source.
36. The power factor correction (PFC) converter in a buck-boost
configuration of claim 29, wherein the constant load current or the
arbitrarily modulated load current flowing through the LED string
is independent from the current flowing through the set-up circuit
and the first level voltage.
37. A power factor correction (PFC) converter in a buck-boost
configuration, comprising: a set-up circuit configured to supply an
input voltage, the set-up circuit comprises: an alternating current
(AC) source; an electromagnetic interference (EMI) filter; and a
diode bridge; a buck transistor connected to the set-up circuit,
and configured to receive a current from the diode bridge; a boost
transistor; a resistor connected to the boost transistor; a coil
that connects the buck transistor and the boost transistor in
series; a first synchronous rectifier connected to the buck
transistor; a second synchronous rectifier connected to the boost
transistor; a buck-boost PFC regulator connected to the set-up
circuit, and configured to regulate a first time pattern of an
on/off status of the buck transistor and the boost transistor and a
second time pattern of an on/off status of the first synchronous
rectifier and the second synchronous rectifier in a synchronous
manner; a capacitor connected to the second synchronous rectifier;
and a load connected to the second synchronous rectifier.
38. The power factor correction (PFC) converter in a buck-boost
configuration of claim 37, wherein the load further comprises: a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series; and a constant current source configured to
maintain a constant load current or an arbitrarily modulated load
current flowing through the LED string.
39. The power factor correction (PFC) converter in a buck-boost
configuration of claim 37, wherein the LED string and the constant
current source are configured to be a low-side connection when the
anode of the LED string is connected to the second synchronous
rectifier, the cathode of the LED string is connected to one end of
the constant current source, and the other end of the constant
current source is connected to ground, and the buck-boost PFC
regulator further comprises: a pair of resistor dividers connected
to the output of the set-up circuit; a reference voltage
corresponding to an intended voltage drop across the constant
current source; an error amplifier (EA) configured to compare the
reference voltage with a second level voltage received at the
cathode of the LED string; a multiplier configured to receive
outputs of the pair of resistor dividers and the EA; an oscillator
and current sense ramp generator configured to receive the output
of the boost transistor; and a pulse width modulation (PWM)
comparator configured to receive outputs of the multiplier and the
oscillator and current sense ramp generator, and a driver that
connects the output of PWM comparator with the buck transistor, the
boost transistor, the first synchronous rectifier, and the second
synchronous rectifier to regulate synchronously the first time
pattern of the on/off status of the buck transistor and the boost
transistor, and the second time pattern of the on/off status of the
first synchronous rectifier and the second synchronous
rectifier.
40. The power factor correction (PFC) converter in a buck-boost
configuration of claim 37, wherein the LED string and the constant
current source are configured to be a high-side connection when one
end of the constant current source is connected to the second
synchronous rectifier, the other end of the constant current source
is connected to the anode of the LED string, and the cathode of the
LED string is connected to ground, and the buck-boost PFC regulator
further comprises: a pair of resistor dividers connected to the
output of the set-up circuit; a reference voltage corresponding to
an intended voltage drop across the constant current source; an
error amplifier (EA) configured to compare the reference voltage
with a second level voltage transmitted by a differential amplifier
(DIF); a multiplier configured to receive outputs of the pair of
resistor dividers and the EA; an oscillator and current sense ramp
generator configured to receive the output of the boost transistor;
and a pulse width modulation (PWM) comparator configured to receive
outputs of the multiplier and the oscillator and current sense ramp
generator, and a driver that connects the output of PWM comparator
with the buck transistor, the boost transistor, the first
synchronous rectifier, and the second synchronous rectifier to
regulate synchronously the first time pattern of the on/off status
of the buck transistor and the boost transistor, and the second
time pattern of the on/off status of the first synchronous
rectifier and the second synchronous rectifier.
41. The power factor correction (PFC) converter in a buck-boost
configuration of claim 39 or 40, wherein if the second level
voltage is less than the reference voltage, the EA amplifies its
output via the multiplier, and the PWM comparator extends the duty
cycle to boost the first level voltage; or if the second level
voltage is greater than the reference voltage, the PWM comparator
shortens the duty cycle to reduce the first level voltage.
42. The power factor correction (PFC) converter in a buck-boost
configuration of claim 37, wherein when the buck transistor and the
boost transistor are synchronously on, the first synchronous
rectifier and the second synchronous rectifier are synchronously
off, and the coil is configured to accumulate current, and when the
buck transistor and the boost transistor are synchronously turned
off, the first synchronous rectifier and the second synchronous
rectifier are synchronously turned on, and the coil is configured
to transmit the accumulated current and output the first level
voltage via the second synchronous rectifier.
43. The power factor correction (PFC) converter in a buck-boost
configuration of claim 37, wherein the buck-boost PFC regulator is
configured to achieve a high power factor correction level by
regulating synchronously the first time pattern of the on/off
status of the buck transistor and the boost transistor, and the
second time pattern of the on/off status of the first synchronous
rectifier and the second synchronous rectifier.
44. The power factor correction (PFC) converter in a buck-boost
configuration of claim 38, wherein the first level voltage is
regulated in a feedback loop comprising the second synchronous
rectifier, the capacitor, the LED string and the constant current
source.
45. The power factor correction (PFC) converter in a buck-boost
configuration of claim 38, wherein the constant load current or the
arbitrarily modulated load current flowing through the LED string
is configured to be independent from the current flowing through
the set-up circuit and the first level voltage.
46. The power factor correction (PFC) converter in a buck-boost
configuration of claim 28, further comprises a plurality of loads
connected to the second diode, wherein the plurality of loads are
connected in parallel, and each of the plurality of loads further
comprises: a light-emitting diode (LED) string comprising a
plurality of diodes connected in series; and a constant current
source configured to maintain a constant load current or an
arbitrarily modulated load current flowing through the LED
string.
47. The power factor correction (PFC) converter in a buck-boost
configuration of claim 46, wherein the plurality of constant load
currents or the arbitrarily modulated load currents flowing through
the plurality of LED strings are configured to be independent from
the current flowing through the set-up circuit and the first level
voltage, and the plurality of constant load currents or the
arbitrarily modulated load currents flowing through the plurality
of LED strings are independent from each other.
48. The power factor correction (PFC) converter in a buck-boost
configuration of claim 46, wherein when the buck transistor and the
boost transistor are synchronously on, the coil is configured to
accumulate received current; and when the buck transistor and the
boost transistor are synchronously off, the coil is configured to
transmit the accumulated current and output the first level voltage
via the second diode.
49. The power factor correction (PFC) converter in a buck-boost
configuration of claim 46, wherein the LED string is configured to
be a low-side connection when the anode of the LED string is
connected to the second diode, the cathode of the LED string is
connected to one end of the constant current source, and the other
end of the constant current source is connected to ground, and the
buck-boost PFC regulator further comprises: a pair of resistor
dividers connected to the output of the set-up circuit; a reference
voltage corresponding to a lowest intended voltage drop across the
plurality of constant current sources; an error amplifier (EA)
configured to compare the reference voltage with a second level
voltage received at the cathode of one of the plurality of the LED
strings; a multiplier configured to receive outputs of the pair of
resistor dividers and the EA; an oscillator and current sense ramp
generator configured to receive the output of the boost transistor;
a pulse width modulation (PWM) comparator configured to receive
outputs of the multiplier and the oscillator and current sense ramp
generator, and a driver that connects the output of PWM comparator
with the buck transistor and the boost transistor to synchronously
regulate the time pattern of the on/off status of the buck
transistor and the boost transistor.
50. The power factor correction (PFC) converter in a buck-boost
configuration of claim 46, wherein the LED string is configured to
be a high-side connection when one end of the constant current
source is connected to the second diode, the other end of the
constant current source is connected to the anode of the LED
string, and the cathode of the LED string is connected to ground,
and the buck-boost PFC regulator further comprises: a pair of
resistor dividers connected to the output of the set-up circuit; a
reference voltage corresponding to a lowest intended voltage drop
across the plurality of constant current sources; an error
amplifier (EA) configured to compare the reference voltage with a
second level voltage transmitted by a differential amplifier (DIF);
a multiplier configured to receive outputs of the pair of resistor
dividers and the EA; an oscillator and current sense ramp generator
configured to receive the output of the boost transistor; a pulse
width modulation (PWM) comparator configured to receive outputs of
the multiplier and the oscillator and current sense ramp generator,
and a driver that connects the output of PWM comparator with the
buck transistor and the boost transistor to synchronously regulate
the time pattern of the on/off status of the buck transistor and
the boost transistor.
51. The power factor correction (PFC) converter in a boost-buck
configuration of claim 49 or 50, wherein if the second level
voltage is less than the reference voltage, the EA amplifies its
output via the multiplier, and the PWM comparator extends the duty
cycle to boost the first level voltage; or if the second level
voltage is greater than the reference voltage, the PWM comparator
shortens the duty cycle to reduce the first level voltage.
52. The power factor correction converter in a buck-boost
configuration of claim 49, further comprises a minimum select unit
configured to select a minimum value from a plurality of voltages
received at the cathodes of the plurality of the LED strings, and
transmit the minimum value to the buck-boost PFC regulator as the
second level voltage.
53. The power factor correction converter in a buck-boost
configuration of claim 50, further comprises a minimum select unit
configured to select a minimum value from a plurality of voltages
received at the anodes of the plurality of the LED strings, and
transmit the minimum value to the buck-boost PFC regulator via the
DIF as the second level voltage.
54. The power factor correction (PFC) converter in a buck-boost
configuration of claim 28, wherein the load further comprises: a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series; a current sense resistor; and an optional
disconnect switch with one end connected to one end of the current
sense resistor.
55. The power factor correction (PFC) converter in a buck-boost
configuration of claim 54, wherein the LED string is configured to
be a low-side connection when the anode of the LED string is
connected to the second diode, the cathode of the LED string is
connected to the other end of the current sense resistor, and the
other end of the optional disconnect switch is connected to ground;
and the buck-boost PFC regulator further comprises: a pair of
resistor dividers connected to the output of the set-up circuit; a
reference voltage corresponding to an intended voltage drop across
the current sense resistor; an error amplifier (EA) configured to
compare the reference voltage with a second level voltage received
at the cathode of the LED string; a multiplier configured to
receive outputs of the pair of resistor dividers and the EA; an
oscillator and current sense ramp generator configured to receive
the output of the boost transistor; a pulse width modulation (PWM)
comparator configured to receive outputs of the multiplier and the
oscillator and current sense ramp generator, and a driver that
connects the output of the PWM comparator with the buck transistor
and the boost transistor to synchronously regulate the time pattern
of the on/off status of the buck transistor and the boost
transistor.
56. The power factor correction (PFC) converter in a buck-boost
configuration of claim 54, wherein the LED string is configured to
be a high-side connection when the other end of the current sense
resistor is connected to the second diode, the other end of the
optional disconnect switch is connected to the anode of the LED
string, and the cathode of the LED string is connected to ground;
and the buck-boost PFC regulator further comprises: a pair of
resistor dividers connected to the output of the set-up circuit; a
reference voltage corresponding to an intended voltage drop across
the current sense resistor; a differential amplifier (DIF)
configured to receive inputs from the first level voltage and the
anode of the LED string, and output a second level voltage; an
error amplifier (EA) configured to compare the reference voltage
with the second level voltage; a multiplier configured to receive
outputs of the pair of resistor dividers and the EA; an oscillator
and current sense ramp generator configured to receive the output
of the boost transistor; a pulse width modulation (PWM) comparator
configured to receive outputs of the multiplier and the oscillator
and current sense ramp generator, and a driver that connects the
output of the PWM comparator with the buck transistor and the boost
transistor to synchronously regulate the time pattern of the on/off
status of the buck transistor and the boost transistor.
57. The power factor correction (PFC) converter in a buck-boost
configuration of claim 55 or 56, wherein if the second level
voltage is less than the reference voltage, the EA amplifies its
output via the multiplier, and the PWM comparator extends the duty
cycle to boost the first level voltage; or if the second level
voltage is greater than the reference voltage, the PWM comparator
shortens the duty cycle to reduce the first level voltage.
Description
FIELD OF INVENTION
[0001] The present invention relates generally to a light emitting
diode (LED) lighting system in the industrial/home lighting field,
and in particular, relates to a power factor correction (PFC)
converter with current regulated output implemented in an LED
lighting system in the industrial/home lighting field.
BACKGROUND OF INVENTION
[0002] The LED device has matured greatly since the time of its
inception over thirty years ago. The semiconductor technology
enables an LED lighting device with orders of magnitude longer life
than the traditional incandescent and fluorescent bulbs. To save
energy and stop global warming, world-wide governments propose
migrating away from the traditional incandescent and fluorescent
bulbs. However, the cost of manufacturing LED lighting devices is
still much higher than the traditional incandescent and fluorescent
bulbs and therefore, becomes an obstacle to the migration. While
the manufacturing cost of the LED lighting devices remains high,
improving the performance of an LED driver; for example, achieving
a high power factor correction value may be an alternative solution
to reducing the cost and facilitating the migration from
traditional lighting devices to LED lighting devices.
[0003] Early stage industry standard for industrial/home LED
lighting drivers simply allows the LED current to be the same as
the alternating current (AC) input current. FIG. 1 is an exemplary
illustration 100 of an LED lighting driver with a same AC current
flowing across an LED string and a coil in the prior art. In
exemplary illustration 100, an AC current from a set-up circuit 101
may flow across an LED string 106 and a coil 108. Therefore, the
current flowing through the LED string 106 is the same as the
current flowing through the coil 108 and the AC current from the
set-up circuit 101. However, in this prior art configuration, the
AC current does not necessarily follow the AC voltage so as to
achieve a high Power Factor level >0.9. When AC current varies
in accordance with the AC line input to the set-up circuit 101,
then such criteria serves to meet the PFC standard (PFC>0.9) for
industrial/home lighting that most countries in the world adopted
since the European Union instituted the IEC555 standard in early
1990s.
[0004] In the early stage technology of the LED lighting driver,
although the average of the LED current may be constant, the
instant LED current varies in a triangular shape, and behaves as a
switching-type current flow in accordance with the AC input
current. FIG. 2 is an exemplary illustration 200 of an LED current
that varies over a wide range with peak and valley levels in the
prior art. In exemplary illustration 200, although the average of
the LED current may be constant, the instant LED current varies in
accordance with the coil current peak and valley values and the LED
current may also vary in a triangular shape, i.e., a switching-type
current flow. Such architecture does not lead to high PFC because
the AC current does not follow the sinusoidal AC voltage line.
[0005] The performance of the LED lighting driver improved in the
past few years by adopting a true PFC stage prior to the LED
current driver. FIG. 3 is an exemplary illustration 300 of another
LED lighting driver with separated AC current and LED current in
the prior art. The exemplary illustration 300 may comprise a set-up
circuit 301, a boost PFC regulator 305, a first coil 308, a first
transistor 310, a first diode 309, a first capacitor 307, an LED
string 321, a second capacitor 320, a second coil 322, a second
diode 323, a second transistor 324 and an LED control 325. The
boost PFC regulator 305 may be implemented to regulate a direct
current (DC) level voltage at the anode of the LED string 321. In
some embodiment, the DC level voltage may refer to a VPFC level
voltage of approximate 400v. The VPFC level voltage may provide
higher tolerance to current variation than the AC line input, and
thus, current flowing through the LED string 321 may no longer be
sensitive to the AC line input and the performance of the LED
string may be increased. This approach increased the performance of
the LED Lighting as a fixed level voltage (VPFC) inputted into the
LED string is no longer sensitive to a varying AC input. Meanwhile,
the industry increased the PFC standard to be higher than 0.9 and
closer to 0.98.
[0006] Recent research shows that the current flowing through LEDs
may be forced to true constant rather than varying around a fixed
average value. Further, dimming capability when the LED current
becomes constant improves the LED performance by at least one order
of magnitude. One example of the above approach is described in
European Publication EP 2315497A1. However, in EP 2315497A1, the
LED string cannot be connected directly to the VPFC level voltage.
Further, U.S. Pat. No. 7,157,809 B2 underlines the problems to
regulate current in non-linear loads and provides a general
solution. U.S. Pat. No. 7,157,809 B2 provides a regulated load/LED
current as long as the current source is maintained with sufficient
headroom from the current source drain to the current source
terminal. Satisfying the headroom requirement guarantees the
load/LED current is constant and independent from the variation of
the output voltage. LED lighting devices may benefit from the above
noted approach because the PFC stage implemented prior to the load
provides a constant level voltage to the LED string and enables the
VPFC to be independent from the AC input. FIG. 4 is an exemplary
illustration 400 of a boost converter with higher output voltage
than input voltage in the prior art. The exemplary illustration 400
of a boost converter may comprise a set-up circuit 401, a boost PFC
regulator 405, a coil 408, a transistor 410, a diode 409 and a
capacitor 407. The boost converter allows the output voltage to be
always higher than the input voltage. Under the circumstances of
the universal range discussed above, the output voltage of the
boost converter may be higher than 276 AC, which has been
standardized to as high as 400v DC. The boost converter in
exemplary illustration 400 has particular advantages in the LED
lighting market because the AC current is always continuous and
makes it easier to follow the AC line voltage. However, a
disadvantage of the exemplary illustration 400 is that there is no
intrinsic current limit and therefore additional circuitry may be
required to limit the inrush current during startup.
[0007] The industry has accustomed to so-called universal line,
where some countries operate at 85 AC while others operate at 276
AC. This is fundamentally 100AC-15%. and 240 AC +15%. Such a wide
range of AC levels must be met via a universal line power supply,
and an LED lighting device has to be designed to fit the
requirement of the wide range. Under the circumstances of the
universal range discussed above, the output voltage of the boost
converter may be higher than 276 AC, which is standardized to as
high as 400v direct current (DC). As illustrated in FIG. 5, the
400v DC level, i.e., VPFC level is applied to the LED string.
However, such applications require a large number of LEDs of
approximately 130 LED diodes, as each LED diode has approximately
3v drop at a room temperature.
SUMMARY OF THE INVENTION
[0008] Accordingly, the present invention is directed to a power
factor correction (PFC) converter with current regulated output in
an LED lighting system substantially obviates one or more problems
due to limitations and disadvantages of the related art.
[0009] In an embodiment, the present invention provides a power
factor correction (PFC) converter in a boost configuration followed
by a buck regulator. The PFC converter in a boost configuration
comprises a set-up circuit configured to supply an input voltage,
the set-up circuit further comprises an alternating current (AC)
source; an electromagnetic interference (EMI) filter; and a diode
bridge; a first coil connected to the set-up circuit, and
configured to receive a rectified current from the diode bridge; a
first transistor connected to the first coil; a boost PFC regulator
configured to regulate a first time pattern of an on/off status of
the first transistor so as to force the AC current to follow the AC
voltage envelope and achieve a high PFC >0.9; a first diode
connected to the first transistor, and configured to output a first
level voltage; a first capacitor connected to the first diode; a
buck converter configured to receive the first level voltage from
the first diode, and convert the first level voltage to a second
level voltage, the buck converter further comprises a second
transistor connected to the first diode; a buck regulator connected
to the second transistor; a second diode connected to the second
transistor; a second coil connected to the second transistor, and
configured to output the second level voltage; a second capacitor
connected to the second coil; and a load connected to the second
coil.
[0010] In some embodiments, the load further comprises a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series; and a constant current source configured to
maintain a constant load current or an arbitrarily modulated load
current flowing through the LED string. When the LED string is
applied as load, this includes linear, logarithmic and pulse width
modulation (PWM) dimming. The number of LEDs in the LED string
determines the voltage at the output of the buck converter.
[0011] In some embodiments, the LED string is configured to be a
low-side connection when the anode of the LED string is connected
to the second coil, the cathode of the LED string is connected to
one end of the constant current source, and the other end of the
constant current source is connected to the ground, and the buck
regulator further comprises a second reference voltage
corresponding to an intended voltage drop across the current
source; a second EA configured to compare the second reference
voltage with a third level voltage received at the cathode of the
LED string in order to keep the constant current source headroom
high enough for proper operation of the current source; a second
oscillator; and a second PWM comparator configured to receive
outputs of the second EA and the second oscillator, and regulate a
second time pattern of the on/off status of the second
transistor.
[0012] In some embodiments, the LED string is configured to be a
high-side connection when one end of the constant current source is
connected to the second coil, the other end of the constant current
source is connected to the anode of the LED string, and the cathode
of the LED string is connected to the ground, and the buck
regulator further comprises a second reference voltage
corresponding to an intended voltage drop across the current
source; a second EA configured to compare the second reference
voltage with a third level voltage transmitted by a differential
amplifier (DIF); a second oscillator; and a second PWM comparator
configured to receive outputs of the second EA and the second
oscillator, and regulate a second time pattern of the on/off status
of the second transistor.
[0013] In some embodiments, if the third level voltage is less than
the second reference voltage, the second EA amplifies its output,
and the second PWM comparator extends a second duty cycle to boost
the second level voltage; or if the third level voltage is greater
than the second reference voltage, the second PWM comparator
shortens the second duty cycle to reduce the second level
voltage.
[0014] In some embodiments, when the first transistor is on, the
first coil is configured to accumulate received current, or when
the first transistor is off, the first coil is configured to
transmit accumulated current and output the first level voltage to
the buck converter via the first diode.
[0015] In some embodiments, the boost PFC regulator is configured
to achieve a high power factor correction level by regulating the
first time pattern of the on/off status of the first transistor, in
such a way that the AC current follows the AC voltage envelope.
[0016] In some embodiments, the second level voltage is regulated
in a feedback loop comprising the buck converter, the LED string
and the constant current source.
[0017] In some embodiments, the second level voltage is independent
of the first level voltage. The second level voltage is determined
by the number of LEDs in the string plus the constant current
source headroom.
[0018] In some embodiments, the constant load current or the
arbitrarily modulated load current flowing through the LED string
is independent of the current flowing through the set-up circuit,
the first level voltage and the second level voltage. This is an
important element that the present invention brings into the state
of the art in order to allow better load current regulation while
still achieving a high PFC.
[0019] In some embodiments, the boost PFC regulator further
comprises a first pair of resistor dividers connected to the output
of the set-up circuit; a second pair of resistor dividers
configured to receive the first level voltage at the output of a
first diode; a first reference voltage corresponding to the first
level voltage at the output of a first diode; a first error
amplifier (EA) configured to compare the first reference voltage
with the first level voltage received at the second pair of
resistor dividers; a multiplier configured to receive outputs of
the first pair of resistor dividers and the first EA; a first
oscillator; and a first pulse width modulation (PWM) comparator
configured to receive outputs of the multiplier and the first
oscillator, and regulate the first time pattern of the on/off
status of the first transistor.
[0020] In some embodiments, if the first level voltage received at
the second pair of resistor dividers is less than the first
reference voltage, the first EA amplifies its output via the
multiplier, and the first PWM comparator extends a first duty cycle
to boost the first level voltage; or if the first level voltage
received at the second pair of resistor dividers is greater than
the first reference voltage, the first PWM comparator shortens the
first duty cycle to reduce the first level voltage. This first
level voltage is about 400v to allow the coverage of Universal AC
line input levels.
[0021] In yet another embodiment, the load further comprises a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series; a current sense resistor; and an optional
disconnect switch with one end connected to one end of the sense
resistor.
[0022] In some embodiments, the LED string is configured to be a
low-side connection when the anode of the LED string is connected
to the second coil, the cathode of the LED string is connected to
the other end of the current sense resistor, and the other end of
the optional disconnect switch is connected to the ground, (please
note that the configuration optional switch followed by current
sense resistor to ground will achieve the same function) and the
buck regulator further comprises a second reference voltage
corresponding to an intended voltage drop across the load; a second
EA configured to compare the second reference voltage with a third
level voltage received at the cathode of the LED string; this third
level voltage equals to the intended LED current times the current
sense resistor; a second oscillator; and a second PWM comparator
configured to receive outputs of the second EA and the second
oscillator, and regulate a second time pattern of the on/off status
of the second transistor.
[0023] In some embodiments, the LED string is configured to be a
high-side connection when the other end of the current sense
resistor is connected to the second coil, the other end of the
optional disconnect switch is connected to the anode of the LED
string, and the cathode of the LED string is connected to the
ground, and the buck regulator further comprises a second reference
voltage corresponding to an intended voltage drop across the
current sense resistor; a second EA configured to compare the
second reference voltage with a third level voltage transmitted by
a differential amplifier (DIF); a second oscillator; and a second
PWM comparator configured to receive outputs of the second EA and
the second oscillator, and regulate a second time pattern of the
on/off status of the second transistor.
[0024] In some embodiments, if the third level voltage is less than
the second reference voltage, the second EA amplifies its output,
and the second PWM comparator extends a second duty cycle to boost
the second level voltage; or if the third level voltage is greater
than the second reference voltage, the second PWM comparator
shortens the second duty cycle to reduce the second level voltage.
In this way, the voltage across the load is adjusted so that the
LED current can be regulated.
[0025] In yet another embodiment, a power factor correction (PFC)
converter in a boost configuration followed by a buck regulator
comprises a set-up circuit configured to supply an input voltage,
the set-up circuit comprises an alternating current (AC) source; an
electromagnetic interference (EMI) filter; and a diode bridge; a
first coil connected to the set-up circuit, and configured to
receive a current from the diode bridge; a first transistor
connected to the first coil; a boost PFC regulator configured to
regulate a first time pattern of the on/off status of the first
transistor; a first synchronous rectifier connected to the first
transistor via a first inverter and configured to output a first
level voltage; a first capacitor connected to the first synchronous
rectifier; a buck converter configured to receive the first level
voltage from the first synchronous rectifier, and convert the first
level voltage to a second level voltage, the buck converter further
comprises a second transistor connected to the first diode; a buck
regulator connected to the second transistor; a second synchronous
rectifier connected to the second transistor via a second inverter;
a second coil connected to the second transistor, and configured to
output the second level voltage; and a second capacitor connected
to the second coil; and a load connected to the second coil.
[0026] In some embodiments, the load further comprises a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series; and a constant current source configured to
maintain a constant load current or an arbitrarily modulated load
current flowing through the LED string. When the LED string is
applied as load, this includes linear, logarithmic and pulse width
modulation (PWM) dimming.
[0027] In some embodiments, the LED string is configured to be a
low-side connection when the anode of the LED string is connected
to the second coil, the cathode of the LED string is connected to
one end of the constant current source, and the other end of the
constant current source is connected to the ground, and the buck
regulator further comprises a second reference voltage
corresponding to an intended voltage drop across the constant
current source; a second EA configured to compare the second
reference voltage with a third level voltage received at the
cathode of the LED string; a second oscillator; and a second PWM
comparator configured to receive outputs of the second EA and the
second oscillator, and regulate a second time pattern of the on/off
status of the second transistor.
[0028] In some embodiments, the LED string is configured to be a
high-side connection when one end of the constant current source is
connected to the second coil, the other end of the constant current
source is connected to the anode of the LED string, and the cathode
of the LED string is connected to the ground, and the buck
regulator further comprises a second reference voltage
corresponding to an intended voltage drop across the constant
current source; a second EA configured to compare the second
reference voltage with a third level voltage; a second oscillator
transmitted by a differential amplifier (DIF); and a second PWM
comparator configured to receive outputs of the second EA and the
second oscillator, and regulate a second time pattern of the on/off
status of the second transistor.
[0029] In some embodiments, if the third level voltage is less than
the second reference voltage, the second EA amplifies its output,
and the second PWM comparator extends a second duty cycle to boost
the second level voltage; or if the third level voltage is greater
than the second reference voltage, the second PWM comparator
shortens the second duty cycle to reduce the second level
voltage.
[0030] In some embodiments, the boost PFC regulator further
comprises a first pair of resistor dividers connected to the output
of the set-up circuit; a second pair of resistor dividers
configured to receive the first level voltage at the output of the
first synchronous rectifier; a first reference voltage
corresponding to the first level voltage at the output of the first
synchronous rectifier; a first error amplifier (EA) configured to
compare the first reference voltage with the first level voltage
received at the second pair of resistor dividers; a multiplier
configured to receive outputs of the first pair of resistor
dividers and the first EA; a first oscillator; and a first pulse
width modulation (PWM) comparator configured to receive outputs of
the multiplier and the first oscillator, and regulate the first
time pattern of the on/off status of the first transistor in order
to force the AC current to follow the AC voltage so as to achieve
high PFC level.
[0031] In some embodiments, if the first level voltage is less than
the first reference voltage, the first EA amplifies its output via
the multiplier, and the first PWM comparator extends a first duty
cycle to boost the first level voltage; or if the first level
voltage is greater than the first reference voltage, the first PWM
comparator shortens the first duty cycle to reduce the first level
voltage.
[0032] In yet another embodiment, the power factor correction (PFC)
converter in a boost configuration followed by a buck regulator
further comprises a plurality of loads connected to the second
coil, where the plurality of loads are connected in parallel, and
each of the plurality of loads further comprises a light-emitting
diode (LED) string comprising a plurality of diodes connected in
series; and a constant current source configured to maintain a
constant load current or an arbitrarily modulated load current
flowing through the LED string. When the LED string is applied as
load, this includes linear, logarithmic and pulse width modulation
(PWM) dimming.
[0033] In some embodiments, the LED string is configured to be a
low-side connection when the anode of the LED string is connected
to the second coil, the cathode of the LED string is connected to
one end of the constant current source, and the other end of the
constant current source is connected to the ground, and the buck
regulator further comprises a second reference voltage
corresponding to a lowest intended voltage drop across the
plurality of loads; a second EA configured to compare the second
reference voltage with a third level voltage from the cathode that
has the lowest voltage drop among the plurality of the LED strings;
a second oscillator; and a second PWM comparator configured to
receive outputs of the second EA and the second oscillator, and
regulate a second time pattern of the on/off status of the second
transistor.
[0034] In some embodiments, the LED string is configured to be a
high-side connection when one end of the constant current source is
connected to the second coil, the other end of the constant current
source is connected to the anode of the LED string, and the cathode
of the LED string is connected to the ground, and the buck
regulator further comprises a second reference voltage
corresponding to a lowest intended voltage drop across the
plurality of loads; a second EA configured to compare the second
reference voltage with a third level voltage transmitted by a
differential amplifier (DIF); a second oscillator; and a second PWM
comparator configured to receive outputs of the second EA and the
second oscillator, and regulate a second time pattern of the on/off
status of the second transistor.
[0035] In some embodiments, the power factor correction (PFC)
converter in a boost configuration followed by a buck regulator
further comprises a minimum select unit configured to select a
minimum value from a plurality of voltages received at the cathodes
of the plurality of the LED strings, and transmit the minimum value
to the second EA as the third level voltage.
[0036] In yet another embodiment, the power factor correction (PFC)
converter in a boost configuration followed by a buck regulator
further comprises a minimum select unit configured to select a
minimum value from a plurality of voltages received at the anodes
of the plurality of the LED strings, and transmit the minimum value
to the second EA via the DIF as the third level voltage.
[0037] In some embodiments, if the third level voltage is less than
the second reference voltage, the second EA amplifies its output,
and the second PWM comparator extends a second duty cycle to boost
the second level voltage; or if the third level voltage is greater
than the second reference voltage, the second PWM comparator
shortens the second duty cycle to reduce the second level
voltage.
[0038] The Boost configuration followed by the Buck driver
described above suffers from complexity and the need for 2
inductors. A large cost is incurred in the magnetic side of power
supplies because of the large volume for the coil and its core.
Reducing the number of coils or even designing away the transformer
down to a single inductor, brings important commercial advantages
(reduced cost, size and assembly).
[0039] The Buck Boost architecture proposed in this invention
achieves at least the Boost Buck performance with a simpler
configuration because it takes advantage of the Buck Boost topology
which allows the 2 converters to merge into a single circuit and
operate around a single coil. Further, advantage of this
architecture is that the regulated voltage is independent of the AC
line level being above or below it and furthermore, the regulated
voltage is determined by the load.
[0040] In a further embodiment, a power factor correction (PFC)
converter in a buck-boost configuration comprises a set-up circuit
configured to supply an input voltage, the set-up circuit comprises
an alternating current (AC) source; an electromagnetic interference
(EMI) filter that; and a diode bridge; a buck transistor connected
to the set-up circuit, and configured to receive a current from the
diode bridge; a first diode connected to the buck transistor; a
boost transistor; a resistor connected to the boost transistor; a
coil that connects the buck transistor and the boost transistor; a
buck-boost PFC regulator connected to the set-up circuit, and
configured to regulate a time pattern of the on/off status of the
buck transistor and the boost transistor synchronously; a second
diode connected to the coil and the boost transistor, and
configured to output a first level voltage; a capacitor connected
to the second diode; and a load connected to the second diode.
[0041] In some embodiments, the load further comprises a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series; and a constant current source configured to
maintain a constant load current or an arbitrarily modulated load
current flowing through the LED string. When the LED string is
applied as load, this includes linear, logarithmic and pulse width
modulation (PWM) dimming.
[0042] In some embodiments, the LED string is configured to be a
low-side connection when the anode of the LED string is connected
to the second diode, the cathode of the LED string is connected to
one end of the constant current source, and the other end of the
constant current source is connected to the ground, and the
buck-boost PFC regulator further comprises a pair of resistor
dividers connected to the output of the set-up circuit; a reference
voltage corresponding to an intended voltage across the constant
current source; the purpose is to maintain enough headroom across
the constant current source to ensure its proper operation; an
error amplifier (EA) configured to compare the reference voltage
with a second level voltage received at the cathode of the LED
string; a multiplier configured to receive outputs of the pair of
resistor dividers and the EA; an oscillator and current sense ramp
generator configured to receive the output of the boost transistor;
a pulse width modulation (PWM) comparator configured to receive
outputs of the multiplier and the oscillator and current sense ramp
generator, and a driver that connects the output of the PWM
comparator with the buck transistor and the boost transistor to
synchronously regulate the time pattern of the on/off status of the
buck transistor and the boost transistor.
[0043] In some embodiments, the LED string is configured to be a
high-side connection when one end of the constant current source is
connected to the second diode, the other end of the constant
current source is connected to the anode of the LED string, and the
cathode of the LED string is connected to the ground, and the
buck-boost PFC regulator further comprises a pair of resistor
dividers connected to the output of the set-up circuit; a reference
voltage corresponding to an intended voltage across the constant
current source; an error amplifier (EA) configured to compare the
reference voltage with a second level voltage transmitted by a
differential amplifier (DIF); a multiplier configured to receive
outputs of the pair of resistor dividers and the EA; an oscillator
and current sense ramp generator configured to receive the output
of the boost transistor; a pulse width modulation (PWM) comparator
configured to receive outputs of the multiplier and the oscillator
and current sense ramp generator, and a driver that connects the
output of the PWM comparator with the buck transistor and the boost
transistor to synchronously regulate the time pattern of the on/off
status of the buck transistor and the boost transistor.
[0044] In some embodiments, if the second level voltage is less
than the reference voltage, the EA amplifies its output via the
multiplier, and the PWM comparator extends the duty cycle to boost
the first level voltage; or if the second level voltage is greater
than the reference voltage, the PWM comparator shortens the duty
cycle to reduce the first level voltage. This adjusts the voltage
across the load in such a way as to maintain enough headroom across
the constant current source in order to ensure its proper
operation. This ensures that the current flowing through the LED
string is well regulated. This adjustment is independent from and
does not impact the operation of the PFC section of the
circuit.
[0045] In some embodiments, when the buck transistor and the boost
transistor are on synchronously, the coil is configured to
accumulate received current; and when the buck transistor and the
boost transistor are off synchronously, the coil is configured to
transmit accumulated current and output the first level voltage via
the second diode so as to allow the AC current to follow the AC
voltage envelope and thus keep high PFC.
[0046] In some embodiments, the buck-boost PFC regulator is
configured to achieve a high power factor correction level by
regulating the time pattern of the on/off status of the buck
transistor and the boost transistor synchronously.
[0047] In some embodiments, the first level voltage is regulated in
a feedback loop comprising the second diode, the capacitor, the LED
string and the constant current source.
[0048] In some embodiments, the constant load current or the
arbitrarily modulated load current flowing through the LED string
is independent from the current flowing through the set-up circuit
and the first level voltage. In some embodiments, the number of
LEDs in the string and the headroom across the constant current
source determine the first voltage level, which is independent of
the AC voltage input.
[0049] In a further embodiment, a power factor correction (PFC)
converter in a buck-boost configuration comprises a set-up circuit
configured to supply an input voltage, the set-up circuit comprises
an alternating current (AC) source; an electromagnetic interference
(EMI) filter; and a diode bridge; a buck transistor connected to
the set-up circuit, and configured to receive an current from the
diode bridge; a boost transistor; a resistor connected to the boost
transistor; a coil that connects the buck transistor and the boost
transistor in series; a first synchronous rectifier connected to
the buck transistor; a second synchronous rectifier connected to
the boost transistor; a buck-boost PFC regulator connected to the
set-up circuit, and configured to regulate a first time pattern of
an on/off status of the buck transistor and the boost transistor
and a second time pattern of an on/off status of the first
synchronous rectifier and the second synchronous rectifier in a
synchronous manner; a capacitor connected to the second synchronous
rectifier; and a load connected to the second synchronous
rectifier.
[0050] In some embodiments, the LED string and the constant current
source are configured to be a low-side connection when the anode of
the LED string is connected to the second synchronous rectifier,
the cathode of the LED string is connected to one end of the
constant current source, and the other end of the constant current
source is connected to the ground, and the buck-boost PFC regulator
further comprises a pair of resistor dividers connected to the
output of the set-up circuit; a reference voltage corresponding to
an intended voltage drop across the constant current source; an
error amplifier (EA) configured to compare the reference voltage
with a second level voltage received at the cathode of the LED
string; a multiplier configured to receive outputs of the pair of
resistor dividers and the EA; an oscillator and current sense ramp
generator configured to receive the output of the boost transistor;
and a pulse width modulation (PWM) comparator configured to receive
outputs of the multiplier and the oscillator and current sense ramp
generator, and a driver that connects the output of PWM comparator
with the buck transistor, the boost transistor, the first
synchronous rectifier, and the second synchronous rectifier to
regulate synchronously the first time pattern of the on/off status
of the buck transistor and the boost transistor, and the second
time pattern of the on/off status of the first synchronous
rectifier and the second synchronous rectifier.
[0051] In some embodiments, the LED string and the constant current
source are configured to be a high-side connection when one end of
the constant current source is connected to the second synchronous
rectifier, the other end of the constant current source is
connected to the anode of the LED string, and the cathode of the
LED string is connected to the ground, and the buck-boost PFC
regulator further comprises a pair of resistor dividers connected
to the output of the set-up circuit; a reference voltage
corresponding to an intended voltage drop across the constant
current source; an error amplifier (EA) configured to compare the
reference voltage with a second level voltage transmitted by a
differential amplifier (DIF); a multiplier configured to receive
outputs of the pair of resistor dividers and the EA; an oscillator
and current sense ramp generator configured to receive the output
of the boost transistor; and a pulse width modulation (PWM)
comparator configured to receive outputs of the multiplier and the
oscillator and current sense ramp generator, and a driver that
connects the output of PWM comparator with the buck transistor, the
boost transistor, the first synchronous rectifier, and the second
synchronous rectifier to regulate synchronously the first time
pattern of the on/off status of the buck transistor and the boost
transistor, and the second time pattern of the on/off status of the
first synchronous rectifier and the second synchronous
rectifier.
[0052] In some embodiments, if the second level voltage is less
than the reference voltage, the EA amplifies its output via the
multiplier, and the PWM comparator extends the duty cycle to boost
the first level voltage; or if the second level voltage is greater
than the reference voltage, the PWM comparator shortens the duty
cycle to reduce the first level voltage. This adjusts the voltage
across the load in such a way as to maintain enough headroom across
the constant current source to ensure its proper operation. This
ensures that the current flowing through the LED string is well
regulated. This adjustment is independent from and does not impact
the operation of the PFC section of the circuit.
[0053] In some embodiments, when the buck transistor and the boost
transistor are synchronously on, the first synchronous rectifier
and the second synchronous rectifier are synchronously off, and the
coil is configured to accumulate current, and when the buck
transistor and the boost transistor are synchronously turned off,
the first synchronous rectifier and the second synchronous
rectifier are synchronously turned on, and the coil is configured
to transmit the accumulated current and output the first level
voltage via the second synchronous rectifier.
[0054] In some embodiments, the buck-boost PFC regulator is
configured to achieve a high power factor correction level by
regulating synchronously the first time pattern of the on/off
status of the buck transistor and the boost transistor, and the
second time pattern of the on/off status of the first synchronous
rectifier and the second synchronous rectifier.
[0055] In some embodiments, the first level voltage is regulated in
a feedback loop comprising the second synchronous rectifier, the
capacitor, the LED string and the constant current source. The
first level voltage is determined by the number of LEDs in the
string plus the head room across the constant current source.
[0056] In some embodiments, the constant load current or the
arbitrarily modulated load current flowing through the LED string
is configured to be independent from the current flowing through
the set-up circuit and the first level voltage.
[0057] In yet another embodiment, the power factor correction (PFC)
converter in a buck-boost configuration further comprises a
plurality of loads connected to the second diode, where the
plurality of loads are connected in parallel, and each of the
plurality of loads further comprises a light-emitting diode (LED)
string comprising a plurality of diodes connected in series; and a
constant current source configured to maintain a constant load
current or an arbitrarily modulated load current flowing through
the LED string. When the LED string is applied as load, this
includes linear, logarithmic and pulse width modulation (PWM)
dimming.
[0058] In some embodiments, when the buck transistor and the boost
transistor are synchronously on, the coil is configured to
accumulate received current; and when the buck transistor and the
boost transistor are synchronously off, the coil is configured to
transmit the accumulated current and output the first level voltage
via the second diode.
[0059] In some embodiments, the plurality of constant load currents
or the arbitrarily modulated load currents flowing through the
plurality of LED strings are configured to be independent from the
current flowing through the set-up circuit and the first level
voltage, and the plurality of constant load currents or the
arbitrarily modulated load currents flowing through the plurality
of LED strings are independent from each other.
[0060] In some embodiments, the LED string is configured to be a
low-side connection when the anode of the LED string is connected
to the second diode, the cathode of the LED string is connected to
one end of the constant current source, and the other end of the
constant current source is connected to the ground, and the
buck-boost PFC regulator further comprises a pair of resistor
dividers connected to the output of the set-up circuit; a reference
voltage corresponding to a lowest intended voltage drop across the
plurality of constant current sources; an error amplifier (EA)
configured to compare the reference voltage with a second level
voltage received at the cathode of one of the plurality of the LED
strings; a multiplier configured to receive outputs of the pair of
resistor dividers and the EA; an oscillator and current sense ramp
generator configured to receive the output of the boost transistor;
a pulse width modulation (PWM) comparator configured to receive
outputs of the multiplier and the oscillator and current sense ramp
generator, and a driver that connects the output of PWM comparator
with the buck transistor and the boost transistor to synchronously
regulate the time pattern of the on/off status of the buck
transistor and the boost transistor.
[0061] In some embodiments, the LED string is configured to be a
high-side connection when one end of the constant current source is
connected to the second diode, the other end of the constant
current source is connected to the anode of the LED string, and the
cathode of the LED string is connected to the ground, and the
buck-boost PFC regulator further comprises a pair of resistor
dividers connected to the output of the set-up circuit; a reference
voltage corresponding to a lowest intended voltage drop across the
plurality of constant current sources; an error amplifier (EA)
configured to compare the reference voltage with a second level
voltage transmitted by a differential amplifier (DIF); a multiplier
configured to receive outputs of the pair of resistor dividers and
the EA; an oscillator and current sense ramp generator configured
to receive the output of the boost transistor; a pulse width
modulation (PWM) comparator configured to receive outputs of the
multiplier and the oscillator and current sense ramp generator, and
a driver that connects the output of PWM comparator with the buck
transistor and the boost transistor to synchronously regulate the
time pattern of the on/off status of the buck transistor and the
boost transistor.
[0062] In some embodiments, if the second level voltage is less
than the reference voltage, the EA amplifies its output via the
multiplier, and the PWM comparator extends the duty cycle to boost
the first level voltage; or if the second level voltage is greater
than the reference voltage, the PWM comparator shortens the duty
cycle to reduce the first level voltage. This allows the system to
keep the lowest voltage constant current source in proper operation
and all other current sources will also have the minimum headroom
covered.
[0063] In some embodiments, the power factor correction converter
in a buck-boost configuration further comprises a minimum select
unit configured to select a minimum value from a plurality of
voltages received at the cathodes of the plurality of the LED
strings, and transmit the minimum value to the buck-boost PFC
regulator as a second level voltage.
[0064] In yet another embodiment, the power factor correction
converter in a buck-boost configuration further comprises a minimum
select unit configured to select a minimum value from a plurality
of voltages received at the anodes of the plurality of the LED
strings, and transmit the minimum value to the buck-boost PFC
regulator via the DIF as a second level voltage.
[0065] In yet another embodiment, the load further comprises a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series; a current sense resistor; and an optional
disconnect switch with one end connected to one end of the current
sense resistor. Note the configuration optional switch followed by
current sense resistor to ground will achieve the same
function.
[0066] In some embodiments, the LED string is configured to be a
low-side connection when the anode of the LED string is connected
to the second diode, the cathode of the LED string is connected to
the other end of the current sense resistor, and the other end of
the optional disconnect switch is connected to the ground, and the
buck-boost PFC regulator further comprises a pair of resistor
dividers connected to the output of the set-up circuit; a reference
voltage corresponding to an intended voltage across the current
sense resistor; an error amplifier (EA) configured to compare the
reference voltage with a second level voltage received at the
cathode of the LED string; a multiplier configured to receive
outputs of the pair of resistor dividers and the EA; an oscillator
and current sense ramp generator configured to receive the output
of the boost transistor; a pulse width modulation (PWM) comparator
configured to receive outputs of the multiplier and the oscillator
and current sense ramp generator, and a driver that connects the
output of the PWM comparator with the buck transistor and the boost
transistor to synchronously regulate the time pattern of the on/off
status of the buck transistor and the boost transistor.
[0067] In some embodiments, the power factor correction converter
in a buck-boost configuration further comprises the LED string is
configured to be a high-side connection when the other end of the
current sense resistor is connected to the second diode, the other
end of the optional disconnect switch is connected to the anode of
the LED string, and the cathode of the LED string is connected to
the ground, and the buck-boost PFC regulator further comprises a
pair of resistor dividers connected to the output of the set-up
circuit; a reference voltage corresponding to an intended voltage
across the current sense resistor; an error amplifier (EA)
configured to compare the reference voltage with a second level
voltage transmitted by a differential amplifier (DIF); a multiplier
configured to receive outputs of the pair of resistor dividers and
the EA; an oscillator and current sense ramp generator configured
to receive the output of the boost transistor; a pulse width
modulation (PWM) comparator configured to receive outputs of the
multiplier and the oscillator and current sense ramp generator, and
a driver that connects the output of the PWM comparator with the
buck transistor and the boost transistor to synchronously regulate
the time pattern of the on/off status of the buck transistor and
the boost transistor.
[0068] In some embodiments, if the second level voltage is less
than the reference voltage, the EA amplifies its output via the
multiplier, and the PWM comparator extends the duty cycle to boost
the first level voltage; or if the second level voltage is greater
than the reference voltage, the PWM comparator shortens the duty
cycle to reduce the first level voltage. This adjusts the voltage
across the load in such a way as to maintain a constant voltage
drop across the current sense resistor, thus ensuring the flow of a
constant current through the load.
BRIEF DESCRIPTION OF THE DRAWINGS
[0069] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention. In the drawings:
[0070] FIG. 1 illustrates an LED lighting driving configuration
with a same AC current flowing across an LED string and a coil in
the prior art;
[0071] FIG. 2 illustrates an LED current that varies over a wide
range with peak and valley levels in the prior art;
[0072] FIG. 3 illustrates another LED lighting driving
configuration with separated AC current and LED current in the
prior art;
[0073] FIG. 4 illustrates a boost converter with higher output
voltage than input voltage in the prior art that is done in order
to achieve high PFC while covering the Universal AC input line
voltage;
[0074] FIG. 5 illustrates an exemplary power factor correction
(PFC) converter in a boost configuration in accordance with the
present invention;
[0075] FIG. 6 illustrates an exemplary embodiment of a power factor
correction (PFC) converter in a boost configuration followed by a
buck regulator with a low-side connected load in accordance with
the present invention;
[0076] FIG. 7 illustrates an exemplary embodiment of a power factor
correction (PFC) converter in a boost configuration followed by a
buck regulator with detailed configuration of a boost PFC
regulator, a buck regulator and a low-side connected load in
accordance with the present invention;
[0077] FIG. 7a illustrates an exemplary embodiment of a power
factor correction (PFC) converter in a boost configuration followed
by a buck regulator using synchronous rectifiers and a low-side
connected load in accordance with the present invention;
[0078] FIG. 8 illustrates an exemplary embodiment of a power factor
correction (PFC) converter in a boost configuration followed by a
buck regulator with detailed configuration of a boost PFC
regulator, a buck regulator and a high-side connected load in
accordance with the present invention.
[0079] FIG. 9 illustrates an exemplary embodiment of a power factor
correction (PFC) converter in a buck-boost configuration with a
low-side connected load in accordance with the present
invention;
[0080] FIG. 9a illustrates an exemplary embodiment of a power
factor correction (PFC) converter in a buck-boost configuration
using synchronous rectifiers and a low-side connected load in
accordance with the present invention;
[0081] FIG. 9b illustrates an exemplary embodiment of a power
factor correction (PFC) converter in a buck-boost configuration
with a high-side connected load in accordance with the present
invention;
[0082] FIG. 10 illustrates an exemplary embodiment of a power
factor correction (PFC) converter in a buck-boost configuration
feeding multiple low side connected loads, each load consisting of
an LED-string and a constant current source in accordance with the
present invention;
[0083] FIG. 11 illustrates an exemplary embodiment of a buck-boost
configuration feeding multiple low side connected loads, each load
consisting of an LED-string and a constant current source; a
minimum select unit sends feedback to the converter in accordance
with the present invention;
[0084] FIG. 12 illustrates an exemplary embodiment of a buck-boost
configuration buck-boost configuration using a current sense
resistor and a low-side connected load in accordance with the
present invention;
[0085] FIG. 12a illustrates an exemplary embodiment of a buck-boost
configuration buck-boost configuration using a current sense
resistor and a high-side connected load in accordance with the
present invention;
[0086] FIG. 13 illustrates an exemplary embodiment of a power
factor correction (PFC) converter in a boost configuration followed
by a buck regulator feeding multiple low side connected loads, each
load consisting of an LED-string and a constant current source; a
minimum select unit sends feedback to the converter in accordance
with the present invention;
[0087] FIG. 14 illustrates an exemplary embodiment of a power
factor correction (PFC) converter in a boost configuration followed
by a buck regulator using a sense resistor and a low-side connected
load in accordance with the present invention; and
DETAILED DESCRIPTION
[0088] Reference will now be made in detail to embodiments,
examples of which are illustrated in the accompanying drawings. In
the following detailed description, numerous non-limiting specific
details are set forth in order to assist in understanding the
subject matter presented herein. It will be apparent, however, to
one of ordinary skill in the art that various alternatives may be
used without departing from the scope of the present invention and
the subject matter may be practiced without these specific details.
For example, it will be apparent to one of ordinary skill in the
art that the subject matter presented herein can be implemented on
any type of power factor correction (PFC) converter with current
regulated output.
[0089] FIG. 5 is an exemplary embodiment 500 of a power factor
correction (PFC) converter in a boost configuration in accordance
with the present invention. The exemplary embodiment 500 may
comprise a set-up circuit 501, a boost PFC regulator 505, a coil
508, a transistor 510, a diode 509, a capacitor 507, an LED string
comprising a plurality of LEDs connected in series and a constant
current source 525. The set-up circuit may further comprise an AC
source, an electromagnetic interference (EMI) filter and a diode
bridge 504. A high DC level of 400v, i.e., VPFC level is outputted
to the anode of the LED string. However, as each LED has
approximate 3v voltage drop at a room temperature, the exemplary
embodiment 500 requires a large number of LEDs to be used in order
to achieve high efficiency. Fewer diodes used in the LED string
would lead to extra voltage drop across the constant current source
which means less efficiency.
[0090] FIG. 6 is an exemplary embodiment of a power factor
correction (PFC) converter in a boost configuration followed by a
buck regulator with a low-side connected load in accordance with
the present invention. This approach improves the solution of FIG.
5 in that a lower number of diodes in the LED string can be used
while still achieving high efficiency since the second coil helps
store energy and avoid losses. The exemplary embodiment 600
comprises a set-up circuit 601, a first coil 608, a first
transistor 610, a boost PFC regulator 605, a first diode 609, a
first capacitor 607, a buck converter 611 and a load 622. The
set-up circuit 601 may further comprise an alternating current (AC)
source 602, an electromagnetic interface (EMI) filter 603, and a
diode 604. The first coil 608 may receive a rectified current from
the diode 604. The boost PFC regulator 605 may regulate a first
time pattern of an on/off status of the first transistor 610. The
buck converter 611 may receive a first level voltage v1 from the
first diode 609 and convert it to a second level voltage v2. The
buck converter 611 may further comprise a second transistor 623, a
buck regulator 624, a second diode 626, a second coil 627 and a
second capacitor 620.
[0091] In some embodiments, the load 622 may further comprise a
light-emitting diode (LED) string 621 comprising a plurality of
diodes connected in series and a constant current source 625
configured to maintain a constant load current or an arbitrarily
modulated load current flowing through the LED string 621. When the
LED string is applied as load, this includes linear, logarithmic
and pulse width modulation (PWM) dimming. In some embodiments, the
load 622 may be configured to be a low-side connection when the
anode of the LED string 621 is connected to the second coil 627,
the cathode of the LED string 621 is connected to one end of the
constant current source 625, and the other end of the constant
current source 625 is connected to the ground. In yet another
embodiments, the load 622 may be configured to be a high-side
connection when one end of the constant current source 625 is
connected to the second coil 627, the other end of the constant
current source 625 is connected to the anode of the LED string 621,
and the cathode of the LED string 621 is connected to the
ground.
[0092] FIG. 7 is an exemplary embodiment of a power factor
correction (PFC) converter in a boost configuration followed by a
buck regulator as illustrated in exemplary embodiment 600 with
detailed configuration of a boost PFC regulator, a buck regulator
and a low-side connected load in accordance with the present
invention. In the exemplary embodiments 700, the boost PFC
regulator 705 may further comprise a first pair of resistor
dividers 741, a second pair of resistor dividers 742, a first
reference voltage 745 corresponding to the first level voltage v1
at the output of a first diode 709, a first error amplifier (EA)
746, a multiplier 747, a first oscillator 744 and a first pulse
width modulation (PWM) comparator 748. An AC voltage from the
set-up circuit 701 may be inputted to the boost PFC regulator 705
via the first pair of resistor dividers 741. The divided voltage
may be applied to the multiplier 747 as one input. The first EA 746
may receive the first level voltage v1 via the second pair of
resistor dividers 742 and compare it with the first reference
voltage 745. If the first level voltage v1 is less than the first
reference voltage, the first EA 746 amplifies its output via the
multiplier 747, and the first PWM comparator 748 extends a first
duty cycle to boost the first level voltage v1; or if the first
level voltage v1 is greater than the first reference voltage, the
first PWM comparator 748 shortens the first duty cycle to reduce
the first level voltage v1. The above regulation scheme of the
boost PFC regulator 705 forces an AC current to follow an AC
voltage in order to achieve a high PFC performance (i.e., a high
PFC level). The high PFC performance that can be achieved is
independent from the load.
[0093] In some embodiments when the load 722 is in low-side
connection, the buck regulator 724 may further comprises a second
reference voltage 734 corresponding to an intended voltage drop
across the constant current source 725, a second EA 732, a second
oscillator 731 and a second PWM comparator 733. The second
reference voltage 734 may be configured to be high enough to keep
the constant current source 725 with sufficient headroom to proper
operation. The second EA 732 may receive a third level voltage v3
at the cathode of the LED string 721 and compare it with the second
reference voltage v2. If the third level voltage v3 is less than
the second reference voltage, the second EA 732 amplifies its
output, and the second PWM comparator 733 extends a second duty
cycle to boost the second level voltage v2 at the anode of the LED
string 722; or if the third level voltage v3 is greater than the
second reference voltage, the second PWM comparator 733 shortens
the second duty cycle to reduce the second level voltage v2. In the
above regulation scheme of the buck regulator 724, the third level
voltage v3 at the cathode of the LED string 721 is fed back into
the second EA 732 to ensure the first level voltage v1 is
sufficiently stepped down to the second level voltage v2 such that
the constant current source 725 has enough headroom voltage not to
get saturated. The second level voltage v2 is determined by the
number of LEDs in the string plus the voltage drop across the
constant current source, thus ensuring high efficiency
operation.
[0094] In some embodiments, there may be more ripple at the output
of the capacitor 720 if the capacitor 720 is configured to be of a
smaller value. The third level voltage v3 at the cathode of the LED
string 721 that is outputted to the negative pin of the EA 732 may
be configured to stay above the headroom voltage including the
presence of ripple. The EA 732 may be configured with a very slow
feedback control loop as to regulate the average of a signal with
such low frequency ripple.
[0095] Alternatively, in yet another embodiment, the load 722 may
be in a high-side connection. FIG. 8 illustrates an exemplary
embodiment of a power factor correction (PFC) converter in a boost
configuration followed by a buck regulator with detailed
configuration of a boost PFC regulator, a buck regulator and a
high-side connected load in accordance with the present invention.
The exemplary embodiment 800 may have the same configuration as the
exemplary embodiment 700 except that the load 722 is in a high-side
connection. The embodiment 800 may further comprise a differential
amplifier (DIF) 728. The DIF 728 may receive inputs from both ends
of the constant current source 725, take the difference between the
inputs, refer the difference to ground, and output the third level
voltage v3 to the second EA 732 for regulation. The regulation
scheme of the buck regulator 724 in the high-side connection
embodiment may be the same as in the low-side connection
embodiment, and may achieve the same benefits as the low-side
connection embodiment.
[0096] In any one of the exemplary embodiment 700 and the exemplary
embodiment 800, when the first transistor 710 is on, the first coil
708 accumulates received current, and when the first transistor 710
is off, the first coil 708 transmits accumulated current and
outputs the first level voltage v1 to the buck converter 711 via
the first diode 709. Such first level voltage v1 is about 400v in
order to cover the Universal AC line input range, and therefore
achieve a high PFC by allowing AC current to follow the AC line
envelope.
[0097] In any one of the exemplary embodiment 700 and the exemplary
embodiment 800, the boost PFC regulator 705 may be configured to
achieve a high power factor correction level by regulating the
first time pattern of the on/off status of the first transistor 710
in order to force the AC current to follow the AC voltage to
achieve a high PFC level. The high power factor correction level
that can be achieved is approximately equal to 0.96 or is greater
than 0.96, and is independent from the load.
[0098] In any one of the exemplary embodiment 700 and the exemplary
embodiment 800, the first level voltage v1 is greater than the
second level voltage v2, and the second level voltage v2 is
independent of the first level voltage v1 and the PFC performance.
The second level voltage v2 is determined by the number of LEDs in
the string plus the voltage drop across the constant current
source.
[0099] In any one of the exemplary embodiment 700 and the exemplary
embodiment 800, the second level voltage v2 may be regulated
according to a number of diodes in the LED string 721, and the
second level voltage v2 may be regulated in a feedback loop
comprising the buck converter 711, the LED string 721 and the
constant current source 725.
[0100] In any one of the exemplary embodiment 700 and the exemplary
embodiment 800, the constant load current or the arbitrarily
modulated load current flowing through the LED string 721 and the
regulation performance of the constant load current or the
arbitrarily modulated load current flowing through the LED string
721 are both independent of the current flowing through the set-up
circuit 701, the first level voltage v1 and the second level
voltage v2 provided that the second level voltage v2 is sufficient
(equal or greater than) to ensure enough headroom across the
constant current source.
[0101] Although the constant current source 725 should be kept with
enough headroom voltage to ensure proper operation, excess headroom
voltage may cause the system to be less efficient. In yet another
embodiment, the first diode 709 and the second diode 726 may be
replaced with two synchronous rectifiers. FIG. 7a illustrates an
exemplary embodiment of a power factor correction (PFC) converter
in a boost configuration followed by a buck regulator using
synchronous rectifiers and a low-side connected load in accordance
with the present invention. The exemplary embodiment 700a may have
the same configuration as the exemplary embodiment 700 except that
the first diode 709 and the second diode 726 may be replaced by a
first synchronous rectifier 709a and a second synchronous rectifier
726a. In the exemplary embodiment 700a, the first synchronous
rectifier 709a may connect to the first transistor 710a via a first
inverter 749a and output the first level voltage v1; and the second
synchronous rectifier 726a may connect to the second transistor via
a second inverter 735a. With proper rectifier sizing for low Rdson,
the voltage drop across the synchronous rectifier may be made
smaller than the voltage drop across the diode, and thus improving
the regulation efficiency.
[0102] The PFC converter in a boost configuration followed by a
buck regulator are advantageous over the prior art at least in that
the load current may be independent of the boost PFC regulator
output VPFC (i.e., the first level voltage v1) and the power factor
correction level when a minimum VPFC condition is satisfied.
Further, the regulation of the load current may be independent of
the boost PFC regulator output VPFC (i.e., the first level voltage
v1) when a minimum VPFC condition is satisfied. Even further,
independent of the PFC value, the regulation performance of the
load current can still be independently pursued.
[0103] In yet another embodiment, the PFC converter in a boost
configuration followed by a buck regulator may have a plurality of
loads. FIG. 13 illustrates an exemplary embodiment 1300 of a power
factor correction (PFC) converter in a boost configuration followed
by a buck regulator using multi-string LEDs and a low-side
connected load in accordance with the present invention. The
exemplary embodiment 1300 may have the same configuration as the
exemplary embodiment 700 except that a plurality of loads is
connected to the buck converter. In the exemplary embodiment 1300,
a plurality of loads 1322, 1352 and 1362 are connected in parallel.
Each of the plurality of loads may further comprise a
light-emitting diode (LED) string comprising a plurality of diodes
connected in series, for example, 1321, 1351 and 1361; and a
constant current source configured to maintain a constant load
current or an arbitrarily modulated load current flowing through
the LED string, for example, 1325, 1355 and 1365. When the LED
string is applied as load, this includes linear, logarithmic and
pulse width modulation (PWM) dimming. A second reference voltage
1334 may correspond to a lowest intended voltage drop across the
plurality of loads 1322, 1352 and 1362.
[0104] In some embodiments when the plurality of loads 1322, 1352
and 1362 is in a low-side connection, the second EA 1332 may
receive a third level voltage v3 via a minimum select unit 1350,
and compare it with the second reference voltage 1334. The minimum
select unit 1350 may receive a plurality of voltage drops at the
cathodes of the plurality of LED string 1325, 1355 and 1365, select
the lowest intended voltage drop across the plurality of constant
current sources, and transmit the lowest intended voltage drop to
the second EA 1332 as the third level voltage v3. If the third
level voltage v3 is less than the second reference voltage 1334,
the second EA 1332 amplifies its output, and the second PWM
comparator extends a second duty cycle to boost the second level
voltage v2; or if the third level voltage v3 is greater than the
second reference voltage, the second PWM comparator 1333 shortens
the second duty cycle to reduce the second level voltage v2.
[0105] Alternatively, in some embodiments, the plurality of loads
1322, 1352 and 1362 may be in a high-side connection. Similar to
the exemplary embodiment 800 when a single load is used, the
embodiment of multi-string LEDs with multiple high-side connected
loads may further comprise a differential amplifier (DIF) to
receive inputs from both ends of one constant current source and
output a third level voltage v3 to the second EA for regulation.
The regulation scheme of the buck regulator in such embodiment may
be the same as in the low-side connection embodiment, and may
achieve the same benefits as the low-side connection
embodiment.
[0106] The exemplary embodiment 1300 of a PFC converter in a boost
configuration followed by a buck regulator using multi-string LEDs
may provide proper load current regulation for all not only one LED
string at all times. Further, the plurality of load currents
flowing through the multiple loads connected in parallel can be set
independently from one another as long as the constant current
source in each LED string has enough headroom to operate
properly.
[0107] In yet another embodiment, the constant current source of
the load in a PFC converter in a boost configuration followed by a
buck regulator may be replaced by a current sense resistor and an
optional disconnect switch. FIG. 14 illustrates an exemplary
embodiment 1400 of a power factor correction (PFC) converter in a
boost configuration followed by a buck regulator using a current
sense resistor and a low-side connected load in accordance with the
present invention. In the exemplary embodiment 1400, the load 1428
may comprise a light-emitting diode (LED) string 1421 comprising a
plurality of diodes connected in series, a current sense resistor
1425 and an optional disconnect switch 1422 with one end connected
to one end of the current sense resistor.
[0108] In some embodiments, the load 1428 may be a low-side
connection when the anode of the LED string 1421 is connected to
the second coil 1427, the cathode of the LED string 1421 is
connected to the other end of the current sense resistor 1425, and
the other end of the optional disconnect switch 1422 is connected
to the ground. The second EA 1432 may receive a third level voltage
v3 at the cathode of the LED string 1421 and compare it with a
second reference voltage 1434 that corresponds to an intended
voltage drop across the current sense resistor 1425. If the third
level voltage v3 is less than the second reference voltage 1434,
the second EA 1432 amplifies its output, and the second PWM
comparator 1433 extends a second duty cycle to boost the second
level voltage v2; or if the third level voltage v3 is greater than
the second reference voltage 1434, the second PWM comparator 1433
shortens the second duty cycle to reduce the second level voltage
v2. The regulation of the second voltage level v2 is achieved when
the load current times the current sense resistor equals to the
second reference voltage 1434.
[0109] Alternatively, in some embodiments, the load 1428 may be a
high-side connection when the other end of the current sense
resistor 1425 is connected to the second coil 1427, the other end
of the optional disconnect switch 1422 is connected to the anode of
the LED string 1421, and the cathode of the LED string 1421 is
connected to ground. Similar to the exemplary embodiment 800 when a
constant current source is used, the embodiment using sense
resistor and a high-side connected load may further comprise a
differential amplifier (DIF) to receive inputs from both ends of
the current sense resistor and output a third level voltage v3 to
the second EA for regulation. The regulation scheme of the buck
regulator in such an embodiment may be the same as in the low-side
connection embodiment, and may achieve the same benefits as the
low-side connection embodiment.
[0110] FIG. 9 illustrates an exemplary embodiment 900 of a power
factor correction (PFC) converter in a buck-boost configuration
with a low-side connected load in accordance with the present
invention. In exemplary embodiment 900, a PFC converter may
comprise a set-up circuit 901, a buck transistor 910, a first diode
909, a boost transistor 923, a resistor 911 configured for
over-current protection, a coil 908, a buck-boost PFC regulator
905, a second diode 926, a capacitor 907 and a load 922. The set-up
circuit 901 may further comprise an AC source 902, an EMI filter
903 and a diode bridge 904. The buck-boost PFC regulator 905 may
regulate a time pattern of an on/off status of the boost transistor
923 and the buck transistor 910 synchronously. The buck transistor
910 may receive a rectified current from the set-up circuit 901. If
the input voltage from the set-up circuit 901 is high, the buck
transistor 910 may step down a high input voltage in a circuitry
comprising the first diode 909 and the coil 908. If the input
voltage from the set-up circuit 901 is low, the buck-boost PFC
regulator 905 may boost the voltage level by accumulating energy in
the coil 908 that may be further transferred to the capacitor 907
via the second diode 926.
[0111] The load 922 may further comprise a light-emitting diode
(LED) string 921 comprising a plurality of diodes connected in
series and a constant current source 925 configured to maintain a
constant load current or an arbitrarily modulated load current
flowing through the LED string 921. When the LED string is applied
as load, this includes linear, logarithmic and pulse width
modulation (PWM) dimming. In some embodiments, the load 922 is
configured to be a low-side connection when the anode of the LED
string 921 is connected to the second diode 926, the cathode of the
LED string 921 is connected to one end of the constant current
source 925, and the other end of the constant current source 925 is
connected to ground. In yet another embodiment, the load 922 is
configured to be a high-side connection when one end of the
constant current source 925 is connected to the second diode 926,
the other end of the constant current source 925 is connected to
the anode of the LED string 921, and the cathode of the LED string
921 is connected to ground.
[0112] In some embodiments, when the buck transistor 910 and the
boost transistor 923 are on synchronously, the coil 908 may
accumulate received current, and when the buck transistor 910 and
the boost transistor 923 are off synchronously, the coil 908 may
transmit accumulated current and output the first level voltage v1
via the second diode 926. The first level voltage v1 may deliver a
high PFC performance (i.e., a PFC level of approximate 0.96), and
the voltage level of v1 may be determined by the load so as to
maintain the regulation performance of the load current flowing
through the LED string and the constant current source.
[0113] In some embodiments, the buck-boost PFC regulator 905 may be
configured to achieve a high power factor correction level by
regulating the time pattern of the on/off status of the buck
transistor 910 and the boost transistor 923 synchronously, and the
high power factor correction level is configured to be
approximately equal to 0.96 or greater than 0.96 in order to force
the AC current to follow the AC voltage to achieve the high PFC
performance. In some embodiments, the high PFC performance that can
be achieved may be independent from the load, and further
independent from the first level voltage v1.
[0114] In some embodiments, the first level voltage v1 may be
regulated according to a number of diodes in the LED string 921,
and may be regulated in a feedback loop comprising the second diode
926, the capacitor 907, the LED string 921 and the constant current
source 925. In some embodiments, the first level voltage v1 may be
independent from the AC input and the current flowing through the
set-up circuit.
[0115] In some embodiments, the load current flowing through the
LED string 921 may be independent from the current flowing through
the set-up circuit 901, the first level voltage v1 and the PFC
performance. In yet another embodiment, the regulation performance
of the load current may be independent from the current flowing
through the set-up circuit 901, the first level voltage v1 and the
PFC performance.
[0116] In some embodiments, the buck-boost PFC regulator 905 may
further comprise a pair of resistor dividers 940, a reference
voltage 945 corresponding to an intended voltage across the load
922, an EA 946, a multiplier 947, an oscillator and current sense
ramp generator 944, a PWM comparator 948 and a driver 949. The
driver 949 connects the output of the PWM comparator 948 with the
buck transistor 910 and the boost transistor 923 to synchronously
regulate the time pattern of an on/off status of the buck
transistor 910 and the boost transistor 923. An AC voltage from the
set-up circuit 901 may be inputted to the buck-boost PFC regulator
905 via the pair of resistor dividers 940. The divided voltage may
be applied to the multiplier 947 as one input. In some embodiments
when the load is in low-side connection, the EA 946 may receive a
second level voltage v2 at the cathode of the LED string 921 and
compare it with the first reference voltage 945. If the second
level voltage v2 is less than the reference voltage 945, the EA 946
amplifies its output via the multiplier 947, and the PWM comparator
948 extends the duty cycle to boost the first level voltage v1; or
if the second level voltage v2 is greater than the reference
voltage 945, the PWM comparator 948 shortens the duty cycle to
reduce the first level voltage v1. The above regulation scheme of
the buck-boost PFC regulator 905 forces the AC current to follow
the AC voltage in order to achieve a high PFC performance (i.e., a
high PFC level). The high PFC performance that can be achieved is
independent from the load. Further, the regulation of the
buck-boost PFC controller 905 may maintain the VPFC output (i.e.,
the first level voltage v1) at an appropriate level in order to
provide enough headroom voltage for the constant current source
925.
[0117] Alternatively, in yet another embodiment, the load 922 may
be in high-side connection. FIG. 9b illustrates an exemplary
embodiment 900b of a power factor correction (PFC) converter in a
buck-boost configuration with a high-side connected load in
accordance with the present invention. The exemplary embodiment
900b may have the same configuration as the exemplary embodiment
900 except that the load 922 is in a high-side connection. The
embodiment 900b may further comprise a differential amplifier (DIF)
928. In the exemplary embodiment 900b, the DIF 928 may receive
inputs from both ends of the constant current source 925, take the
difference between the inputs, refer the difference to ground, and
output the third level voltage v3 to the EA 946 for regulation. The
regulation scheme of the buck-boost PFC regulator 905 in exemplary
embodiment 900b may be the same as the regulation scheme in the
low-side connected exemplary embodiment 900, and may achieve the
same benefits as the low-side connected exemplary embodiment
900.
[0118] The PFC converter in a buck-boost configuration is
advantageous over the prior art at least in that the regulation of
the VPFC output (i.e., the first level voltage v1) may be separated
from the regulation of the load current. The power factor may be
corrected to a high PFC level regardless of the VPFC level. In some
embodiments, a minimum VPFC level may be determined by a number of
LEDs 921 in the LED string 925 and a headroom voltage that is
desired for the constant current source 925. Therefore, provided
that the minimum VPFC condition is satisfied, the load current and
the regulation of the load current may be configured to be both
independent from the VPFC level. Further, provided that the minimum
VPFC condition is satisfied, the load current and the regulation of
the load current may be configured to be both independent from the
PFC level. Even further, although the PFC Converter in a buck-boost
configuration is simplified significantly, the regulation
performance of the load current can still be independently
pursued.
[0119] Further, the PFC Converter in a buck-boost configuration is
advantageous over the PFC Converter in a boost configuration
followed by a buck regulator at least in that less circuitry
elements are implemented, and only one coil is required to achieve
the regulation performance. The PFC Converter in a buck-boost
configuration can achieve the same high PFC level as the PFC
Converter in a boost configuration followed by a buck regulator;
and at the meantime, regulate the output of the buck-boost PFC
regulator to satisfy the minimum VPFC condition necessary to
provide enough headroom voltage for the constant current
source.
[0120] In yet another embodiment, the first diode 909 and the
second diode 926 of the PFC converter in a buck-boost configuration
may be replaced with two synchronous rectifiers. FIG. 9a
illustrates an exemplary embodiment 900a of a power factor
correction (PFC) converter in a buck-boost configuration using
synchronous rectifiers in accordance with the present invention.
The exemplary embodiment 900a may have the same configuration as
the exemplary embodiment 900 except that the first diode 909 and
the second diode 926 are replaced with a first synchronous
rectifier 909a and the second synchronous rectifier 926a,
respectively. In exemplary embodiment 900a, the buck transistor
910a, the boost transistor 923a, the first synchronous rectifier
909a and the second synchronous rectifier 926a may all connect to
the driver 949a. When the buck transistor 910a and the boost
transistor 923a are synchronously on, the first synchronous
rectifier 909a and the second synchronous rectifier 926a are
synchronously off, and the coil 908a may accumulate current, and
when the buck transistor 910a and the boost transistor 923a are
synchronously turned off, the first synchronous rectifier 909a and
the second synchronous rectifier 923a are synchronously turned on,
and the coil 908a may transmit the accumulated current; and output
the first level voltage v1 via the second synchronous rectifier
926a. With proper rectifier sizing for low Rdson, the voltage drop
across the synchronous rectifier may be made smaller than the
voltage drop across the diode, and thus improving the regulation
efficiency.
[0121] In some embodiments, the buck-boost PFC regulator 905a may
be configured to achieve a high power factor correction level by
regulating synchronously the first time pattern of the on/off
status of the buck transistor 910a and the boost transistor 923a,
and the second time pattern of the on/off status of the first
rectifier 909a and the second rectifier 926a in order to force the
AC current to follow the AC voltage to achieve the high PFC
performance. In some embodiments, the high power factor correction
level is approximately equal to 0.96 or greater than 0.96.
[0122] In some embodiments, the first level voltage v1 is regulated
in a feedback loop comprising the second rectifier 926a, the
capacitor 907a, the LED string 921a and the constant current source
925a.
[0123] In some embodiments, the PFC converter in a buck-boost
configuration using synchronous rectifiers as illustrated in
exemplary embodiment 900a may achieve the same benefits as the PFC
converter in a buck-boost configuration as illustrated in exemplary
embodiment 900.
[0124] In some embodiments when the load 922a is in a low-side
connection, the EA 946a may receive a second level voltage v2 from
the cathode of the LED string 921a and compare it with the
reference voltage 945a. If the second level voltage v2 is less than
the reference voltage 945a, the EA 946a amplifies its output via
the multiplier 947a, and the PWM comparator 948a extends the duty
cycle to boost the first level voltage v1; or if the second level
voltage v2 is greater than the reference voltage 945a, the PWM
comparator 948a shortens the duty cycle to reduce the first level
voltage v1. Alternatively, in some embodiments when the load 922a
is in high-side connection, the voltages at both ends of the
constant current source 925a are outputted to a differential
amplifier (DIF). The DIF may further output the second level
voltage v2 to the EA 946a for regulation. The regulation scheme of
the PFC converter in a buck-boost configuration using synchronous
rectifiers and a high-side connected load may be the same as the
PFC converter in a buck-boost configuration using synchronous
rectifiers and a low-side connected load illustrated in FIG. 9a,
and may achieve the same benefits as the PFC converter in a
buck-boost configuration using synchronous rectifiers and a
low-side connected load.
[0125] In some embodiments, the PFC converter in a buck-boost
configuration may comprise a plurality of loads. FIG. 10
illustrates an exemplary embodiment 1000 of a power factor
correction (PFC) converter in a buck-boost configuration using
multi-string LEDs and multiple low-side connected loads in
accordance with the present invention. The exemplary embodiment
1000 may have the same configuration as the exemplary embodiment
900 except that a plurality of loads are connected to the second
diode. In the exemplary embodiment 1000, a plurality of loads 1022,
1052, 1062 and 1072 are connected in parallel. Each of the
plurality of loads may further comprise a light-emitting diode
(LED) string comprising a plurality of diodes connected in series,
for example, 1021, 1051, 1061 and 1071; and a constant current
source configured to maintain a constant load current or an
arbitrarily modulated load current flowing through the LED string,
for example, 1025, 1055, 1065 and 1075. When the LED string is
applied as load, this includes linear, logarithmic and pulse width
modulation (PWM) dimming. A reference voltage 1045 may correspond
to a lowest intended voltage drop across the plurality of loads
1022, 1052, 1062 and 1072.
[0126] In some embodiments when the plurality of loads 1022, 1052,
1062 and 1072 are in a low-side connection, the EA 1046 may receive
a second level voltage v2 at the cathode of one of the plurality of
LED string 1021, 1051, 1061 and 1071, and compare it with the
reference voltage 1045. If the second level voltage v2 is less than
the reference voltage 1045, the EA 1046 amplifies its output, and
the PWM comparator 1048 extends a duty cycle to boost the first
level voltage v1; or if the second level voltage v2 is greater than
the reference voltage 1045, the PWM comparator 1048 shortens the
duty cycle to reduce the first level voltage v1.
[0127] Alternatively, in some embodiments, the plurality of loads
1022, 1052, 1062 and 1072 may be in a high-side connection, and the
voltage received at the anode of one of the plurality of LED string
1021, 1051, 1061 and 1071 are used for regulation. Similar to the
exemplary embodiment 900b when a single load is used, the
embodiment of multi-string LEDs with multiple high-side connected
loads may further comprise a differential amplifier (DIF) to
receive inputs from both ends of one constant current source and
output a second level voltage v2 to the EA for regulation. The
regulation scheme of the buck-boost PFC regulator in such
embodiment may be the same as in the low-side connection
embodiment, and may achieve the same benefits as the low-side
connection embodiment.
[0128] In exemplary embodiment 1000 of a PFC converter in a
buck-boost configuration using multi-string LEDs, the plurality of
load currents flowing though the loads may be controlled
separately, and the plurality of load currents may be independent
from one another. Further, the plurality of load currents may be
independent from the VPFC regulation loop. Even further, the
exemplary embodiment 1000 may achieve the same high PFC level and
other similar benefits as the exemplary embodiment 900. In some
embodiments, the exemplary embodiment 1000 may require that the
VPFC level be high enough to provide the voltage drop across the
LED string in addition to the headroom voltage across the constant
current source for each of the plurality of loads.
[0129] In yet another embodiment, the PFC converter in a buck-boost
configuration with a plurality of loads may further comprise a
minimum select unit. FIG. 11 illustrates an exemplary embodiment
1100 of a buck-boost configuration using multi-string LEDs, a
minimum select unit and multiple low-side connected loads in
accordance with the present invention. The exemplary embodiment
1100 may have the same configuration as FIG. 10 except that a
minimum select unit may be connected to the cathodes of the
plurality of LED strings. In exemplary embodiment 1100, the
plurality of loads are in low-side connection, a minimum select
unit 1150 may select a minimum value from a plurality of voltages
received at the cathodes of the plurality of the LED strings 1121,
1151, 1161 and 1171, and transmit the minimum value to the
buck-boost PFC regulator 1105 as a second level voltage v2.
Alternatively, in some embodiment when the plurality of loads are
in high-side connection, the minimum select unit 1150 may select a
minimum value from a plurality of voltages received at the anodes
of the plurality of the LED strings 1121, 1151, 1161 and 1171, and
transmit the minim value via a differential amplifier (DIF) to the
buck-boost PFC regulator for regulation. The operation of the DIF
may be the same as in exemplary embodiment 900b, and may achieve
similar benefits as in the low-side connection embodiment.
[0130] The exemplary embodiment 1100 improves the performance of
the exemplary embodiment 1000. The voltages across the plurality of
the LED strings and constant current sources are compared against
one another, and a smallest headroom voltage is detected. The
smallest headroom voltage is fed back to the buck-boost PFC
regulator for regulation. The exemplary embodiment 1100 improves
the system efficiency by maintaining the outputted VPFC level at a
minimum level necessary for proper system operation, thus minimizes
the headroom loss inherently applied to all the loads attached to
the minimum select unit.
[0131] In yet another embodiment, the constant current source of
the PFC converter in a buck-boost configuration may be replaced
with a current sense resistor and an optional disconnect switch.
FIG. 12 illustrates an exemplary embodiment 1200 of a buck-boost
configuration buck-boost configuration using a current sense
resistor and a low-end connected load in accordance with the
present invention. The exemplary embodiment 1200 may have the same
configuration as the exemplary embodiment 900 except that the
constant current source is replaced with a current sense resistor
1225 and an optional disconnect switch 1222. In the exemplary
embodiment 1200, the load 1228 may comprise a light-emitting diode
(LED) string 1221 comprising a plurality of diodes connected in
series, a current sense resistor 1225 and an optional disconnect
switch 1222 with one end connected to one end of the sense
resistor.
[0132] In the exemplary embodiment 1200, the load is configured to
be a low-side connection. The anode of the LED string 1221 is
connected to the second diode 1226, the cathode of the LED string
1221 is connected to the other end of the current sense resistor
1225, and the other end of the optional disconnect switch 1222 is
connected to ground. The EA 1246 may receive a second level voltage
v2 at the cathode of the LED string 1221 and compare it with a
reference voltage 1245 that corresponds to an intended voltage drop
across the current sense resistor. If the second level voltage v2
is less than the reference voltage 1245, the EA 1246 amplifies its
output via the multiplier 1247, and the PWM comparator 1248 extends
the duty cycle to boost the first level voltage v1, or if the
second level voltage v2 is greater than the reference voltage 1245,
the PWM comparator 1248 shortens the duty cycle to reduce the first
level voltage v1. The regulation of the first voltage level v1 is
achieved when the load current times the current sense resistor
equals to the reference voltage 1245.
[0133] In yet another embodiment, the load may be in high-side
connection. FIG. 12a illustrates an exemplary embodiment 1200a of a
buck-boost configuration buck-boost configuration using a current
sense resistor with the load and a high-side connected load in
accordance with the present invention. In exemplary embodiment
1200a, the other end of the current sense resistor 1225 is
connected to the second diode 1226, the other end of the optional
disconnect switch 1222 is connected to the anode of the LED string
1221, and the cathode of the LED string 1221 is connected to
ground. The exemplary embodiment 1200a may further comprise a
differential amplifier (DIF) 1228. The DIF 1228 may receive inputs
from both ends of the current sense resistor 1225, take the
difference between the inputs, refer the difference to ground, and
output a second level voltage v2 to the EA 1246 for regulation. The
regulation scheme of the high-side connection embodiment may be the
same as the low-side connection embodiment, and may achieve the
same benefits as the low-side connection embodiment.
[0134] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *